This application is based on Application No. 2001-180166, filed in Japan on Jun. 14, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to an electronic control system for controlling an intake air quantity in an internal combustion engine for a motor vehicle with a throttle valve operated by an electric motor with improved control performance while ensuring enhanced fail-safe. More particularly, the present invention is concerned with an intake air quantity control system for an internal combustion engine of the type in which a pair of central processing units or microprocessors (hereinafter referred to as the CPU in abbreviation) are employed for effectuating primary or main controls such as ignition control and fuel supply control for the internal combustion engine (hereinafter also referred to simply as the engine) with the control functions being efficiently and effectively shared between the paired CPUs for improving the control performance.
Further, the present invention is concerned with an intake air quantity control system equipped with a default position restoring mechanism which is so designed as to allow the throttle valve to be automatically restored to a position corresponding to an opening degree slightly greater than that in an idle operation upon breaking or turn-off of a load relay through which an electric power is supplied to the throttle valve control motor, wherein a backup function (fail-safe control) is adopted for coping with abnormality which may possibly occur upon restoration to the default throttle position to thereby realize the intake air quantity control with high control performance and reliability, ensuring thus improved fail-safe feature.
2. Description of Related Art
In general, the electronic throttle control for controlling the opening degree of the throttle valve through which the intake air is fed to the engine in dependence on the depression stroke or degree of an accelerator pedal is extensively adopted in practical applications. In recent years, the intake air quantity control system for the engine of wireless type in which the accelerator pedal wire is spared has been widespread.
Additionally, such intake air quantity control system for the engine has been proposed in which the accelerator pedal wire is used jointly as a backup means or in which the accelerator pedal wire is used in the ordinary driving operation whereas an electric motor is used in a constant-speed operation, e.g. a cruising operation.
On the other hand, the control for the engine system as a whole can be classified into a main control for engine driving machinery (i.e., devices or machines having direct relevancy to the operation of the engine) such as an ignition coil, a fuel injection solenoid valve and the like and an auxiliary equipment control for peripheral equipments such as an electromagnetic valve for a transmission, an electromagnetic clutch for an air-conditioner and the like. Under the circumstances, there have been proposed various types of intake air quantity control systems which differ from one another in respect to what sort of CPU configuration is to be adopted in combination with the control of the throttle valve.
For having better understanding of the concept underlying the present invention, description will first be made of the background techniques. FIG. 9 of the accompanying drawings is a block diagram showing only schematically a general arrangement of a conventional intake air quantity control system for an internal combustion engine which system is designed to perform all controls for the engine by using a single CPU 600a. 
Referring to FIG. 9, output signals 610a of various sensors indicating operation states of the engine are inputted to the CPU 600a. As the various sensor output signals 610a, there may be mentioned such on/off signals and analogue signals which are derived, respectively, from the outputs of an engine rotation speed detecting sensor, a crank angle sensor, an air flow sensor for measuring the intake air quantity (i.e., flow rate of the intake air), an intake pressure sensor, an exhaust gas sensor, a water temperature sensor, an accelerator pedal position sensor (hereinafter also referred to as the APS in abbreviation) for measuring the degree of depression of an accelerator pedal, a throttle position sensor (hereinafter also referred to as the TPS in short) for measuring or detecting the opening degree of a throttle valve, a shift position sensor for detecting a position of a speed shift lever and others.
The CPU 600a is so designed or programmed as to output control signals 620a and 621a for various types of actuators which the engine is equipped with. The control signal 620a is destined for controlling operations of primary or main machinery such as an ignition coil, a fuel injection solenoid valve, a speed stage shifting solenoid valve and an exhaust gas recirculation (EGR) controlling solenoid valve as well as auxiliary equipments such as an air-conditioner and the like. On the other hand, the control signal 621a is destined for the control of a throttle valve control motor or the like.
Incidentally, the conventional system known heretofore for performing all the controls with the single CPU 600a, as shown in FIG. 9, is disclosed in, for example, Japanese Patent Application Laid-Open Publications Nos. 176141/1990 (JP-A-2-176141) and 141389/1999 (JP-A-11-141389).
However, the conventional systems such as mentioned above suffers a serious problem that an excessively heavy burden is imposed on the CPU 600a for realizing satisfactorily the desired engine performance as well as the specified functions and that adequate fail-safe function can not always be ensured for coping with abnormal events occurring in the engine system.
As is well known in the art, so long as the intake air quantity can be controlled with high reliability, there will arise no fear of runaway of the engine. Accordingly, the control of the intake air quantity (i.e., control of flow rate of the intake air) is one of the most important factors for ensuring the safety for operation of the engine. Under the circumstances, it is desirable to provide the relevant sensors and the CPUs in a duplexed arrangement (redundant arrangement) especially for the electronic control of the throttle valve.
FIG. 10 is a block diagram showing schematically a first conventional intake air quantity control system for an internal combustion engine which system is implemented in a triplex CPU configuration in which three CPUs 600b, 601b and 602b are employed for the control purpose.
Referring to FIG. 10, inputted to the CPU 600b are various sensor signals 610b relevant to the main machinery (and auxiliary equipments) from the engine speed detecting sensor, the crank angle sensor, the air flow sensor, the intake pressure sensor and the like. The CPU 600b is so programmed as to generate control signals 620b for the main machinery (and the auxiliary equipment) on the basis of the input sensor signals.
On the other hand, inputted to the CPU 601b are sensor signals 611b for the throttle control from the accelerator pedal position sensor (APS), the throttle position sensor (TPS) and the like. In response to these sensor signals, the CPU 601b outputs a control signal 621b for the throttle valve control motor.
Furthermore, a sensor signal 612b for supervisory control is inputted to the CPU 602b which is so programmed as to output a control signal 622b destined for the supervisory control of a load relay, an electromagnetic clutch and others with the aim of ensuring high fail-safe or security for the electronic control of the throttle valve.
The conventional system in which a plurality of CPUs are employed as in the case of the system shown in FIG. 10 is disclosed in e.g. Japanese Patent Application Laid-Open Publications Nos. 278502/1994 (JP-A-6-278502) and 2152/1999 (JP-A-11-2152).
In these publications, no specific description is found concerning the CPU 600b. It can however be understood that the CPU 601b serves as the main CPU with the CPU 602b serving as the subsidiary CPU dedicated solely for the control of the throttle valve.
The system disclosed in the publications mentioned just above is realized as a combination of the engine control apparatus of accelerator pedal wire type and an additional constant-speed control apparatus by employing three CPUS, which involves consequently high complexity and expensiveness in the system configuration.
FIG. 11 is a block diagram showing schematically a third conventional intake air quantity control system for an internal combustion engine which system includes a pair of CPUs 600c and 601c for the control of the intake air quantity.
Referring to FIG. 11, various sensor signals 610c relevant to the main machinery (and auxiliary equipments) are inputted to the CPU 600c which is programmed to output control signals 620c destined for the main machinery (and the auxiliary equipments).
On the other hand, inputted to the CPU 601c are the sensor signals for the throttle control (and sensor signals for the supervisory control or function) 611c, wherein the CPU 601c is programmed to output a control signal 621c for the throttle valve control motor (and a control signal for the supervisory control or function). Further, the CPUs 600c and 601c are designed to perform mutual monitor functions.
In the CPU configuration shown in FIG. 11, the CPU 600c serves as an engine control unit (ECU in abbreviation) with the CPU 601c serving as a throttle control unit (TCU in short). Thus, the whole system can ensure improved or enhanced security or fail-safe feature by virtue of the mutual monitoring feature.
The system in which a pair of CPUs are employed, as shown in FIG. 11, is disclosed in the Japanese Patent Application Laid-Open Publications Nos. 270488/1996 (JP-A-8-270488) and 97087/2000 (JP-A12-97087). More specifically, a system in which the accelerator pedal wire is employed in combination is disclosed in Japanese Patent Application Laid-Open Publication No. 270488/1996, while a system of wireless implementation type is disclosed in Japanese Patent Application Laid-Open Publication No. 97087/2000.
In both the systems disclosed in the above-mentioned publications, description is found concerning a fail-safe control means for enabling smoothly a so-called limp-home driving (siding operation or go-home operation) upon occurrence of abnormal event(s).
Among the first to third conventional systems mentioned above by reference to FIGS. 9 to 11, the system in which the single CPU 600a is employed as in the case of the system shown in FIG. 9 suffers problems in respect to the security (fail-safe function) and large burden imposed on the CPU 600a for realizing the intended control.
The problems mentioned above can certainly be disposed of by sharing the control functions between or among a plurality of CPUs while allowing mutual surveillance to be effectuated, as mentioned above by reference to FIGS. 10 and 11. However, in view of the fact that the engine drive controls (e.g. ignition control and fuel injection control) and the throttle control bear very intimate relevancy to each other, it is not expedient to share these controls between or among the individual CPUs.
In this conjunction, it is that the various sensor signals inputted to the CPUs contain many sensor signals used in common for the individual controls such as the engine drive control, the throttle valve control and the auxiliary equipment control in addition to the sensor signals destined discretely for these controls, respectively.
Accordingly, inputting directly these common sensor signals individually to each of the CPUs will wastefully incur increase in the number of input ports, to a disadvantage.
As is apparent from the foregoing, the conventional intake air quantity control system for the engine can not evade the problem that difficulty is encountered in ensuring the security (fail-safe) while a heavy burden is imposed on the CPU in performing the intended controls in the case where the single CPU is resorted to.
On the other hand, in the system where a plurality of CPUs 600b to 602b (see FIG. 10) are employed, the engine drive control and the throttle valve control which bear close relevancy to each other are shared by the CPUs 600b and 601b. As a consequence, a large number of input ports are wastefully required, giving rise to the problem of inexpediency.
Similarly, in the system shown in FIG. 11 where a plurality of CPUs 600c and 601c are used, the engine drive control and the throttle valve control are shared discretely by the CPUs 600c and 601c, respectively, incurring a problem that the number of the input ports increases wastefully.
In the light of the state of the art described above, it is an object of the present invention to provide an intake air quantity control system for an internal combustion engine which system includes a pair of so-called main and subsidiary CPUs arranged to share control functions therebetween in such a manner that an engine drive control (main machinery control) and a throttle control are performed by a main CPU while a supervisory control is performed by a subsidiary CPU and in which an abnormality supervising means and a fail-safe control means suited for a novel CPU configuration are incorporated, to thereby ensure significantly enhanced control performance as well as improved fail-safe or security feature.
Another object of the present invention is to provide an intake air quantity control system for an internal combustion engine equipped with a default position restoring mechanism which is so designed as to allow a throttle valve to automatically restore a position corresponding to an opening degree slightly greater than that in an idle operation upon breaking or turn-off of a load relay through which an electric power is supplied to the throttle valve control motor, wherein a backup function (fail-safe control) is ensured for coping with abnormal event(s) possibly occurring upon restoration to the default throttle position to thereby realize the intake air quantity control which can enjoy high performance and security or fail-safe feature.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a first general aspect of the present invention an intake air quantity control system for an internal combustion engine, which system includes a throttle valve control motor for controlling an opening degree of a throttle valve for thereby adjustably regulating a quantity of intake air supplied to the internal combustion engine in dependence on a depression degree of an accelerator pedal, an engine driving machinery including an fuel injection solenoid valve of the internal combustion engine, a load relay through which an electric power is supplied to the throttle valve control motor, peripheral auxiliary equipments of the internal combustion engine, an alarm display device, a main CPU for supplying a first control signal to the throttle valve control motor and second control signals to the engine driving machinery, a subsidiary CPU for supplying a load relay driving signal to the load relay and third control signals to the peripheral auxiliary equipments through cooperation with the main CPU, a first group of on/off sensors for supplying to the main CPU a first group of on/off signals for high-speed/high-frequency operations having relevancy to the first and second control signals, a first group of analogue sensors for supplying a first group of analogue signals to the main CPU, a second group of on/off sensors for supplying to the subsidiary CPU a second group of on/off signals for low-speed/low-frequency operations having relevancy to at least one of the first, second and third control signals, a second group of analogue sensors for supplying a second group of analogue signals to the subsidiary CPU, a serial interface means for enabling signals to be transferred between the main CPU and the subsidiary CPU, an abnormal event storing device for storing detection of an abnormal event to thereby electrically deenergize the load relay while electrically energizing the alarm display device, a power switch for supplying an electric power to at least one of the main CPU and the subsidiary CPU, and a power supply detecting means operative in response to closing or opening of the power switch, wherein the abnormal event storing device is reset by the power supply detecting means.
By virtue of the arrangement of the intake air quantity control system described above, transaction or transfer of the control signals having mutual relevancy or correlated can be facilitated, whereby abnormality supervising means and fail-safe control means suited for the novel CPU configuration can be realized for ensuring enhanced control/response performances. Further, since the subsidiary CPU contributes to reduction of the number of input/output ports of the main CPU and the burden imposed on the main CPU which is in charge of supervising or monitoring unitarily and uniformly high-speed operations, the system can be implemented in the form of a small-size integrated circuit which can nevertheless ensure high safety or fail-safe. More specifically, since such arrangement can be adopted that a large number of input/output signals are caused to pass through the subsidiary CPU, the subsidiary CPU is in the position to supervise the signals for the auxiliary machinery controls inclusive of the throttle valve control. Thus, the burden imposed on the main CPU can effectively be reduced while high security can be ensured for the engine system as a whole. Furthermore, because a large number of signals are transferred between the main CPU and the subsidiary CPU via the serial interfaces, the number of input/output terminals of the main CPU can remarkably be decreased, which in turn means that the intake air quantity control system can be implemented as a small IC chip while allowing logic circuits to be added for further improving the functions and performance of the main CPU when occasion requires.
In a preferred mode for carrying out the invention, the first group of analogue sensors may include a first accelerator pedal position sensor for detecting the depression degree of the accelerator pedal, and a first throttle position sensor for detecting the opening degree of the throttle valve. Similarly, the second group of analogue sensors may include a second accelerator pedal position sensor for detecting the depression degree of the accelerator pedal, and a second throttle position sensor for detecting the opening degree of the throttle valve. In that case, signals indicative of the depression degree of the accelerator pedal and the opening degree of the throttle valve may be respectively inputted to the main CPU and the subsidiary CPU.
Owing to the arrangement described above, the main CPU 111 can perform the throttle valve control by itself, the state of which can be monitored or supervised by the subsidiary CPU by itself. Besides, owing to duplex or duplicate arrangement of the analogue sensors, the intake air quantity control system ensuring the further enhanced fail-safe feature can be realized.
In another preferred mode for carrying out the invention, the intake air quantity control system for the internal combustion engine may further include a wire-breakage/short-circuit detecting means for detecting occurrence of wire-breakage/short-circuit abnormality in the throttle valve control motor to thereby generate a wire-breakage/short-circuit abnormality detection signal, and a watchdog timer circuit for monitoring runaway of the main CPU on the basis of a watchdog signal generated by the main CPU. In that case, the watchdog timer circuit may be so designed as to generate a first reset signal for reactivating the main CPU upon occurrence of abnormality in the watchdog signal generated by the main CPU. On the other hand, the main CPU may be so designed as to generate a second reset signal for reactivating the subsidiary CPU upon occurrence of abnormality in a watchdog signal generated by the subsidiary CPU. In that case, the abnormal event storage device can be set in response to the wire-breakage/short-circuit abnormality detection signal and the first and second reset signals.
With the arrangement described above, when a malfunction temporarily occurs in the CPUs due to noise or the like, a normal state can immediately be restored. Thus, the ignition control and the fuel injection control can normally be carried out substantially continuously. Besides, upon occurrence of runaway of the CPU operation due to noise or the like disturbance, the throttle valve control which plays an essential role in securing the safety for the running operation of a motor vehicle can be stopped while allowing the throttle valve control to be restored upon closing of the power switch. Thus, security can be ensured for the driving of the motor vehicle. Moreover, a message indicative of occurrence of abnormal or erroneous operation can be issued to operator or driver of the motor vehicle.
In yet another preferred mode for carrying out the invention, the intake air quantity control system for the internal combustion engine may further include a first sensor abnormality detecting means for generating a first sensor abnormality detection signal in response to occurrence of the wire-breakage/short-circuit abnormality of the first and second accelerator pedal position sensors and relative output abnormality thereof, and a second sensor abnormality detecting means for generating a second sensor abnormality detection signal in response to occurrence of the wire-breakage/short-circuit abnormality of the first and second throttle position sensors and relative output abnormality thereof, wherein the abnormal event storage device is set in response to the first and second abnormality detection signals.
With the arrangement described above, safety can be ensured by detecting positively the fail abnormality of the sensors relating to the throttle valve control and stopping the throttle valve control which bears great relevancy to the safety of running operation of the motor vehicle. Besides, the operator or the driver can immediately recognize occurrence of the abnormality.
In still another preferred mode for carrying out the invention, at least one of the first and second groups of analogue sensors may include a throttle position sensor for detecting the opening degree of the throttle valve. The main CPU may be so designed as to arithmetically determine a first target throttle opening degree as a target value for the opening degree of the throttle valve while the subsidiary CPU may be so designed as to arithmetically determine a second target throttle opening degree as a target value for the opening degree of the throttle valve, wherein the subsidiary CPU may include an earlier-half control abnormality detecting means for deciding validity of the first target throttle opening degree through comparison of a signal indicative of the first target throttle opening degree with a signal indicative of the second target throttle opening degree, and a latter-half control abnormality detecting means for deciding the validity of the first target throttle opening degree through comparison of the signal indicative of the first target throttle opening degree with a detection signal outputted from the second throttle position sensor and inputted to the subsidiary CPU. In that case, the abnormal event storage device can be set in response to an earlier-half abnormality detection signal generated by the earlier-half control abnormality detecting means and a latter-half abnormality detection signal generated by the latter-half control abnormality detecting means.
With the arrangement described above, abnormal operations of the CPUs, abnormality of the sensors bearing important relevancy to the throttle valve control and abnormality of the throttle valve control motor can be checked synthetically and duplicatively (i.e., during the earlier-half and latter-half periods, respectively), whereby the throttle valve control playing an essential role in securing the safety can be stopped upon detection of the abnormality. Of course, such abnormality can immediately be informed to the operator or driver.
In a further preferred mode for carrying out the invention, at least one of the first and second groups of analogue sensors includes a throttle position sensor for detecting the opening degree of the throttle valve. In that case, the intake air quantity control system may further include a brake switch for detecting a depressed state of a brake pedal to thereby generate a brake application detecting signal, a default position restoring mechanism for causing the throttle valve to be automatically restored to a position at which the opening degree of the throttle valve is slightly greater than that in an idle operation mode of the internal combustion engine, when the power supply to the throttle valve control motor is interrupted, an engine rotation repressing means for adjustably regulating a fuel quantity supplied through the fuel injection solenoid valve in response to deviation of an actual rotation speed of the internal combustion engine from a predetermined threshold value of the rotation speed of the engine upon electrical deenergization of the load relay, a default restoration confirming means responsive to a detection signal of the throttle position sensor for deciding whether the opening degree of the throttle valve is restored to a predetermined position to thereby generate a default restoration signal, an ordinary threshold value setting means for setting an ordinary threshold value on the basis of the default restoration signal and the brake application detecting signal when the default position is restored or alternatively when the brake is inoperative, and a minimum threshold value setting means for setting a minimum threshold value on the basis of the default restoration signal and the brake application detecting signal when the opening degree of the throttle valve is large in the state restored to the default position and when the brake switch is operative, wherein the predetermined threshold value is variably set by the ordinary threshold value setting means and the minimum threshold value setting means in response to the default restoration signal and the brake application detecting signal.
With the arrangement described above, the throttle valve is caused to restore the default position when the load relay is electrically deenergized in response to occurrence of abnormality. Thus, the siding operation can be performed with safety solely by applying the brake. Additionally, in the case where the throttle valve is locked at the position corresponding to a very large opening degree because of a mechanical abnormality (machine malfunction), the motor vehicle can be stopped without any difficulty or alternatively the siding operation thereof can easily be carried out.
According to a second general aspect of the invention, there is provided an intake air quantity control system for an internal combustion engine which comprises an intake air quantity control system for an internal combustion engine includes a throttle valve control motor for controlling an opening degree of a throttle valve for thereby adjustably regulating a quantity of intake air supplied to the internal combustion engine in dependence on a depression degree of an accelerator pedal, a load relay for supplying an electric power to the throttle valve control motor, an accelerator pedal position sensor for detecting the depression degree of the accelerator pedal, a throttle position sensor for detecting the opening degree of the throttle valve, a brake switch for detecting a depressed state of a brake pedal to thereby generate a brake application detecting signal, a default position restoring mechanism for causing the throttle valve to be automatically restored to a position at which the opening degree of the throttle valve is slightly greater than that in an idle operation mode of the internal combustion engine, when the power supply to the throttle valve control motor is interrupted, an engine rotation repressing means for adjustably regulating a fuel quantity supplied through the fuel injection solenoid valve in response to deviation of an actual rotation speed of the internal combustion engine from a predetermined threshold value of the rotation speed of the engine upon deenergization of the load relay, a default restoration confirming means responsive to a detection signal of the throttle position sensor for deciding whether the opening degree of the throttle valve is restored to a predetermined position to thereby generate a default restoration signal, an ordinary threshold value setting means for setting an ordinary threshold value on the basis of the default restoration signal and the brake application detecting signal when the default position is restored or alternatively when the brake is inoperative, and a minimum threshold value setting means for setting a minimum threshold value on the basis of the default restoration signal and the brake application detecting signal when the opening degree of the throttle valve is large in the state restored to the default position and when the brake switch is operative, wherein the predetermined threshold value is variably set by the ordinary threshold value setting means and the minimum threshold value setting means in response to the default restoration signal and the brake application detecting signal.
With the arrangement described above, the throttle valve is caused to restore the default position when the load relay is electrically deenergized in response to occurrence of abnormality. Thus, the siding operation can be performed with safety solely by applying the brake. Besides, in the case where the throttle valve is locked at the position corresponding to a very large opening degree because of a mechanical abnormality, the motor vehicle can be stopped without any difficulty. Alternatively, the siding operation thereof can be carried out.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.